2,698 research outputs found
Spin transport properties of a quantum dot coupled to ferromagnetic leads with noncollinear magnetizations
A correct general formula for the spin current through an interacting quantum
dot coupled to ferromagnetic leads with magnetization at an arbitrary angle
is derived within the framework of the Keldysh formalism. Under
asymmetric conditions, the spin current component J_{z} may change sign for
. It is shown that the spin current and spin tunneling
magnetoresistance exhibit different angle dependence in the free and Coulomb
blockade regimes. In the latter case, the competition of spin precession and
the spin-valve effect could lead to an anomaly in the angle dependence of the
spin current.Comment: 7 pages, 4 figures; some parts of the text has been revised in this
version accepted by J. Phys.: Condens. Matte
Valence bond spin liquid state in two-dimensional frustrated spin-1/2 Heisenberg antiferromagnets
Fermionic valence bond approach in terms of SU(4) representation is proposed
to describe the frustrated Heisenberg antiferromagnetic (AF)
model on a {\it bipartite} square lattice. A uniform mean field solution
without breaking the translational and rotational symmetries describes a
valence bond spin liquid state, interpolating the two different AF ordered
states in the large and large limits, respectively. This novel
spin liquid state is gapless with the vanishing density of states at the Fermi
nodal points. Moreover, a sharp resonance peak in the dynamic structure factor
is predicted for momenta and in the strongly
frustrated limit , which can be checked by neutron
scattering experiment.Comment: Revtex file, 4 pages, 4 figure
PRED(TAP): a system for prediction of peptide binding to the human transporter associated with antigen processing
BACKGROUND: The transporter associated with antigen processing (TAP) is a critical component of the major histocompatibility complex (MHC) class I antigen processing and presentation pathway. TAP transports antigenic peptides into the endoplasmic reticulum where it loads them into the binding groove of MHC class I molecules. Because peptides must first be transported by TAP in order to be presented on MHC class I, TAP binding preferences should impact significantly on T-cell epitope selection. DESCRIPTION: PRED(TAP )is a computational system that predicts peptide binding to human TAP. It uses artificial neural networks and hidden Markov models as predictive engines. Extensive testing was performed to valid the prediction models. The results showed that PRED(TAP )was both sensitive and specific and had good predictive ability (area under the receiver operating characteristic curve Aroc>0.85). CONCLUSION: PRED(TAP )can be integrated with prediction systems for MHC class I binding peptides for improved performance of in silico prediction of T-cell epitopes. PRED(TAP )is available for public use at [1]
State estimation from pair of conjugate qudits
We show that, for parallel input states, an anti-linear map with respect
to a specific basis is essentially a classical operator. We also consider the
information contained in phase-conjugate pairs , and prove
that there is more information about a quantum state encoded in phase-conjugate
pairs than in parallel pairs.Comment: 4 pages, 1 tabl
Microembossing of ultrafine grained Al: microstructural analysis and finite element modelling
Ultra fine grained (UFG) Al-1050 processed by equal channel angular pressing (ECAP) and UFG Al-Mg-Cu-Mn processed by high pressure torsion (HPT) were embossed at both room temperature and 300 °C, with the aim of producing micro-channels. The behaviour of Al alloys during the embossing process was analysed using finite element (FE) modelling. The cold embossing of both Al alloys is characterised by a partial pattern transfer, a large embossing force, channels with oblique sidewalls and a large failure rate of the mould. The hot embossing is characterised by straight channel sidewalls, fully transferred patterns and reduced loads which decrease the failure rate of the mould. Hot embossing of UFG Al-Mg-Cu-Mn produced by HPT shows a potential of fabrication of microelectromechanical system (MEMS) components with micro channels
Optimal entanglement witnesses based on local orthogonal observables
We show that the entanglement witnesses based on local orthogonal observables
which are introduced in [S. Yu and N.-L. Liu, Phys. Rev. Lett. 95, 150504
(2005)] and [O. G\"uhne, M. Mechler, G. T\'oth and P. Adam, Phys. Rev. A 74,
010301 (2006)] in linear and nonlinear forms can be optimized, respectively. As
applications, we calculate the optimal nonlinear witnesses of pure bipartite
states and show a lower bound on the I-concurrence of bipartite higher
dimensional systems with our method.Comment: 6 pages, 1 figure; minor changes, references adde
Improving Convection Parameterization Using ARM Observations and NCAR Community Atmosphere Model
Highlight of Accomplishments: We made significant contribution to the ASR program in this funding cycle by better representing convective processes in GCMs based on knowledge gained from analysis of ARM/ASR observations. In addition, our work led to a much improved understanding of the interaction among aerosol, convection, clouds and climate in GCMs
Quantum phase transition of Bose-Einstein condensates on a ring nonlinear lattice
We study the phase transitions in a one dimensional Bose-Einstein condensate
on a ring whose atomic scattering length is modulated periodically along the
ring. By using a modified Bogoliubov method to treat such a nonlinear lattice
in the mean field approximation, we find that the phase transitions are of
different orders when the modulation period is 2 and greater than 2. We further
perform a full quantum mechanical treatment based on the time-evolving block
decimation algorithm which confirms the mean field results and reveals
interesting quantum behavior of the system. Our studies yield important
knowledge of competing mechanisms behind the phase transitions and the quantum
nature of this system.Comment: 12 pages, 7 figure
Poynting vector, energy density and energy velocity in anomalous dispersion medium
The Poynting vector, energy density and energy velocity of light pulses
propagating in anomalous dispersion medium (used in WKD-like experiments) are
calculated. Results show that a negative energy density in the medium
propagates along opposite of incident direction with such a velocity similar to
the negative group velocity while the direction of the Poynting vector is
positive. In other words, one might say that a positive energy density in the
medium would propagate along the positive direction with a speed having
approximately the absolute valueof the group velocity. We further point out
that neither energy velocity nor group velocity is a good concept to describe
the propagation process of light pulse inside the medium in WKD experiment
owing to the strong accumulation and dissipation effects.Comment: 6 page
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